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Degrees of Placenta Previa

The placenta, the organ that nourishes a developing baby, arises at about two weeks post-conception with the embryo's implantation in the wall of the uterus. If implantation happens too low in the mother's womb, the placenta may grow near or over her cervix. This condition, called placenta previa, happens in one of every 200 pregnancies. Traditionally, doctors have identified four degrees or types of placenta previa, although this classification is changing as of 2011. Placenta previa can cause serious problems like hemorrhage, premature birth and even maternal or fetal death. Its chief warning sign is "painless, bright red vaginal bleeding in the second half of pregnancy," according to MayoClinic.com. Seek your doctor's help with any concerns you may have.

  1. Low-Lying Implantation

    • In low-lying (lateral) implantation, or Type 1 placenta previa, the placenta is low in the uterus, but 2.1 to 3.5cm away from the cervix. In 90 percent of cases, the fetus and placenta migrate up the uterus before the third trimester and before any problems arise. Although they may experience bleeding after birth, women in the remaining 10 percent generally have no symptoms during pregnancy. Vaginal delivery may be possible.

    Marginal Implantation

    • With marginal implantation, also called incomplete or Type 2 placenta previa, the placenta does not grow over the cervix, but is as close as 0.1 to 2.0cm from it. The closer the placenta is to the cervix, the greater the likelihood of problems. However, just like many women with low-lying implantation, many with marginal implantation can deliver vaginally.

    Partial Previa

    • In partial or Type 3 placenta previa, the placenta overlaps the cervix. According to medical consensus, vaginal delivery is too risky for both mother and child. A Cesarean section performed by a skilled obstetrician is recommended, generally at 36 to 38 weeks. However, because of severe bleeding or other complications, some Cesareans need to be performed even earlier.

    Total Previa

    • In total, also called complete, central or Type 4 placenta previa, the placenta covers the entire cervix, even during the phase of labor when the mother's cervix fully dilates (opens). As with partial previa, Cesarean section, generally from 36 to 38 weeks, is necessary to safeguard the lives of both mother and baby.

    Newer Classification Scheme

    • New ultrasound technology allows for more precise diagnosis, more frequent monitoring and better treatment of placenta previa than ever. Although doctors still widely classify placenta previa into the long-established four degrees or types, in 2011 they often describe the condition as "major" or "minor." Minor placenta previa encompasses types 1 and 2, and major types 3 and 4. Doctors generally find that half of all cases are major, and half minor.

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